Field
Implementations of the present disclosure generally relate to the separation of production fluids into oil and water phases and more particularly to the demulsification of heavy crude oils by centrifuge.
Description of the Related Art
Emulsion is defined as a system in which one liquid is relatively distributed or dispersed, in the form of droplets, in another substantially immiscible liquid. In production and flow assurance, the two commonly encountered emulsion types are water droplets dispersed in the oil phase and termed water-in-oil emulsion (W/O) and if the oil is the dispersed phase, it is termed oil-in-water (O/W) emulsion. In crude oil production from brown fields or heavy oil, there is often production of water-in-oil emulsions.
To properly evaluate the properties of water-in-oil emulsions in a laboratory setting, the water needs to be separated out without changing the composition of the oil. Water-in-oil emulsions are typically separated by centrifuge. A centrifuge puts an object in rotation about a fixed axis, applying a force perpendicular to the axis where the centripetal acceleration causes denser substances to separate out along the radial direction, the bottom of the tube and lighter objects tend to move to the top of the tube. However, in most cases, the oil cannot be cleaned by centrifuge as the contrast of density between the water phase and the oil phase does not exist.
To solve this problem, laboratories have developed combined methods that separate water-in-oil emulsions by centrifuge in combination with additional physical and/or chemical treatment. For example, centrifuging while heating the oil sample, centrifuging in the presence of surfactants, or centrifuging in the presence of various solvents. However, these methods typically compromise the heavy oil sample by changing its composition, changing its physical properties like viscosity and density and removing the light hydrocarbon (e.g., C1-C7 hydrocarbons) portions of the sample. Typically, methods that use centrifugation in combination with heat cause the loss of light hydrocarbons (e.g., C1-C7 hydrocarbons) and change the composition of the oil. Methods that use solvents in combination with centrifugation compromise the composition of the oil sample rendering the sample a non-representative sample. Thus, these methods fail to provide a representative oil sample for analysis of oil composition, physical properties and geochemical properties.
Therefore there is a need for methods that separate water-in-oil emulsions in a laboratory setting without physically or chemically altering the oil phase to produce a representative clean heavy oil sample.